Catalysts for use in organic compound transformation reactions

ABSTRACT

A novel catalyst for transforming organic compounds is described. The catalyst is composed of a support selected from refractory oxides such as aluminas, silicas, silica-aluminas or magnesia, used alone or as a mixture, a group VIII metal such as palladium, associated or not associated with another metal, said catalyst being such that the volume of chemisorbed carbon monoxide is greater than or equal to 180 cm 3  per gram of metal and has a programmed temperature reduction profile comprising a single hydrogen consumption peak.

The present invention relates to a novel catalyst comprising at leastone support and at least one metal from group VIII of the periodictable. This catalyst can also contain another metal selected from thegroup formed by alkali metals and/or a metalloid such as sulphur and/orany other chemical element such as a halogen or a halogenated compound.

Control of the textural characteristics of metal particles deposited ona support has been the subject of numerous studies in the literature andcontinues to be the centre of interest in recent research. Particlesize, for example, is a determining factor when a catalyst is used in areaction qualified as “structure sensitive” as defined by Boudart. Achemical transformation is termed “structure sensitive” if the reactionrate (or turn over frequency¹) is dependent on metal crystallite size,in the case of monometallic catalysts, or on the surface composition forbimetallic catalysts. Similarly, the electronic state of the metalconstituting the active surface site will set the adsorption energy ofthe reactants and as a result, the catalytic performances (activity,selectivity and stability). The literature contains many examples ofstudies aimed at establishing the structure sensitivity or insensitivityof a given reaction: hydrogenation of linear or cyclic alkenes² ³ on Ptor Pd based catalysts (insensitive reaction), hydrogenation of alkynesand diolefins⁴ (sensitive reactions), hydrogenolysis of C—C bonds inparaffin or naphthene compounds⁵ ⁶.

¹ The turn over frequency is defined as the rate of reaction reduced tothe number of surface metal atoms.

² J. C. Schlatter, M. Boudart, J. Catal., 24, 1972, 482.

³ M. Boudart, W. C. Cheng, J. Catal., 106, 1987, 134.

⁴ S. Hub, L. Hilaire, R. Touroude, Appl. Catal. 36, 1992, 307.

⁵ J. Barbier, P. Marecot, Nouv. J. Chim. 5, 1981, 393.

⁶ J. R. Anderson, Y. Shymoyama, Proc 5^(th) Int. Cong. Catal., PalmBeach, 1972, North Holland Publ. Co/Amer. Elsevier, Vol 1, 1973, 55.

The formulation of catalysts used in hydrocarbon conversion processeshas formed the subject of a large number of studies. Supported metalcatalysts containing a metal phase based on palladium or nickelsupported on a refractory oxide type support such as alumina arecurrently used in gasoline hydrogenation reactions, for example.

For reactions termed structure sensitive reactions, the protocol forpreparing the catalysts is particularly important and aimed at obtainingan optimum size for the metal particles corresponding to the maximumreaction rate. Thus in the case of the selective hydrogenation ofbutadiene, the most active catalyst must contain particles of about 40Å.

However, the “structure sensitive” nature of a reaction imposing a setparticle size which is in general relatively large (several tens ofAngströms) substantially limits the metal surface exposed per unit massof metal, limiting the catalytic activity as a result.

The present invention shows that it is possible to prepare catalystscontaining at least one metal from group VII of the periodic table ofthe elements which perform particularly well. The size of the metalparticles is generally below 10 Å, which means that the majority of themetal atoms deposited on the support are exposed to the reactants. Thesecatalysts are characterized by volumes of chemisorbed CO of at least 180cm³ per gram of metal, corresponding to a dispersion⁷ of 80% or more.Characterization by programmed temperature reduction (PTR) of this typeof catalyst produces a single hydrogen consumption peak centred on arange of temperature of 50° C. to 300° C. (preferably 100° C. to 200°C.). Hydrogen salting-out is not observed at low temperatures (about 70°C.), salting-out generally being associated with the formation of metalhydrides and characterized in PTR by an intense hydrogen productionsignal at about T=70° C.

⁷ Metallic dispersion is defined as the ratio of the number of metalatoms exposed on the surface to the total number of metal atoms.

The volume of chemisorbed carbon monoxide is generauy measured using thefollowing procedure: after treatment at 200° C. in a stream of hydrogenfor 2 hours, then in helium for 2 hours, it is allowed to cool down toambient temperature, keeping it in helium, before injecting a knownvolume of CO. The CO consumption is followed by gas phasechromatography.

The PTR analysis procedure is based on measuring the quantity ofhydrogen consumed by reduction of the metallic phase as a function oftemperature. The PTR profile obtained thus shows the intensity ofreduction as a function of temperature. Integrating the reduction peaksgives the quantity of hydrogen consumed. The procedure includes in-siture-oxidation, generally by prior calcining at 200° C. for two hours witha temperature rise of 5° C./min. After re-oxidation, the samples arereduced, from ambient temperature up to 900° C., by increasing thetemperature at 5° C./min in a gas stream constituted by 5% hydrogen and95% argon, injected at a flow rate of 20 cm³/min.

Another characterization technique for characterizing the nature of theinteractions between the metal and the support consists in EXAFS (for“Extended X-ray Absorption Fine Structure). In fact, this spectroscopictechnique enables the direct determination (in terms of nature andnumber) of the elements located in the vicinity of a given element. Itis thus possible to know the environment of the metal deposited by anypreparation method.

The hydrocarbon conversion processes for which the catalysts of theinvention are applicable operate at a temperature in the range 10° C. to800° C. and at a pressure in the range 0.1 to 10 HPa.

More particularly, the catalysts of the present invention areapplicable:

to catalytic purification of olefin cuts by selective hydrogenation. Theconditions generally used for this type of transformation are an averagetemperature in the range from 25° C. to 200° C., a pressure in the range0.1 to 10 MPa and a molar ratio of hydrogen to hydrocarbons in the range1 to 150. The feed is generally a steam cracking, cut containing 5 to 12carbon atoms per molecule;

to catalytic hydrogenolysis processes carried out in the range 400° C.to 800° C., at a pressure in the range 0.1 to 2 MPa and with a molarratio of hydrogen to hydrocarbons of 0 to 20;

to hydrogenation processes for hydrocarbons containing alkyne, diene orolefin functions, or aromatic functions, under conditions which areknown to the skilled person, more particularly an average temperature inthe range 10° C. to 400° C. and at a pressure in the range 0.1 to 10MPa; and

to processes for hydrogenation of organic functions such as aldehyde,ketone, ester, acid or nitro functions, under conditions which are knownto the skilled person, more particularly an average temperature in therange 10° C. to 500° C. and at a pressure in the range 0.1 to 10 MPa.

The support for the catalyst of the invention comprises at least onerefractory oxide which is generally selected from oxides of metals fromgroups IIA, IIIA, IVB and IVA of the periodic table of the elements,such as magnesium, aluminum, silicon, titanium, zirconium or thoriumoxides, used alone or as a mixture or mixed with oxides of other metalsfrom the periodic table. Activated carbon can also be used. Type X, Y,mordenite, faujasite, ZSM-5, ZSM-4, ZSM-8, etc. type zeolites ormolecular sieves, also mixtures of metal oxides from groups IIA, IIIA,IVB and/or IVA with a zeolitic material can also be used.

For hydrocarbon transformation reactions, the preferred support isalumina, with a specific surface area which is advantageously in therange 5 to 400 m²/gram, preferably in the range 5 to 150 m²/gram.

Preferred supports used for transforming organic functions are silica,carbon and alumina.

In the catalyst of the invention, the group VIII metal is usuallyselected from iridium, nickel, palladium, platinum, rhodium andruthenium. Platinum and palladium are the preferred metals for thehydrocarbon conversion reactions. Rhodium and ruthenium are thepreferred metals for transforming functional molecules (fine chemicals).The percentage by weight is selected so as to be between 0.01% and 10%,preferably between 0.1% and 5%. The catalyst can also contain anadditional element selected from the group formed by alkali metals,alkaline-earth metals and metalloids (such as sulphur). The percentageby weight is selected so as to be between 0.01% and 10%, preferably inthe range 0.02% to 5%.

The catalyst can be prepared by different procedures for impregnatingthe support and the invention is not limited to a particularimpregnation procedure. When a plurality of solutions is used,intermediate drying and/or calcining can be carried out.

The catalytic metal precursor can be selected from the group formed byformed by the hydroxide, halogenated compounds, nitrate, acetate andchloride of the metal under consideration.

In a preferred preparation technique of the invention, the catalyst isobtained by impregnating the support using an aqueous solution of atleast one group VIII metal compound, the volume of the solutioncorresponding to the retention volume of the support. The impregnatedsupport is then dried and calcined in air, normally between 100° C. andabout 500° C., then reduced in hydrogen at a temperature which isnormally in the range from about 100° C. to about 600° C., preferably inthe range from about 150° C. to about 300° C.

This reduction can be carried out immediately after calcining, or laterat the user's location. It is also possible to directly reduce the driedproducts at the user's location.

The complete description of all applications, patents and publicationscited above and below, and of the corresponding French application97/10878, filed on Aug. 29^(th) 1997, is hereby included by reference inthe present description.

The following examples illustrate the invention without in any waylimiting its scope.

EXAMPLE 1 (reference)

A catalyst A was prepared by impregnating an alumina support with apalladium nitrate solution. This support was in the form of 2 to 4 mmdiameter beads. It had a specific surface area of 65 m²/g and its porevolume was 0.6 ml/g. After impregnation, the catalyst was dried at 120°C. and calcined at 450° C. The palladium content of catalyst A was 0.3%by weight.

EXAMPLE 2 (in accordance with the invention)

A catalyst B was prepared by impregnating an alumina support with asolution containing palladium nitrate and sodium nitrite. This supportwas in the form of 2 to 4 mm diameter beads. It had a specific surfacearea of 139 m²/g and its pore volume was 1.05 ml/g. After impregnation,the catalyst was dried at 120° C. and calcined at 200° C. The palladiumcontent of catalyst B was 0.3% by weight.

EXAMPLE 3 (in accordance with the invention)

A catalyst C was prepared by impregnating an alumina support with asolution containing palladium nitrate and sodium nitrite. This supportwas in the form of 2 to 4 mm diameter beads. It had a specific surfacearea of 39 m/g and its pore volume was 0.57 ml/g. After impregnation,the catalyst was dried at 120° C. and calcined at 200° C. The palladiumcontent of catalyst C was 0.3% by weight.

EXAMPLE 4 (reference)

A catalyst D was prepared by impregnating an alumina support with anexcess of a solution of palladium acetylacetonate in toluene. Thissupport was in the form of 2 to 4 mm diameter beads. It had a specificsurface area of 39 m²/g and its pore volume was 0.57 ml/g. Afterimpregnation, the catalyst was washed with a toluene solution then driedat 120° C. and calcined for 2 hours at 450° C. in a stream of air. Thepalladium content of catalyst D was 0.3% by weight.

EXAMPLE 5 (reference)

Example 4 was repeated, with using an alumina support having a specificsurface area of 139 m²/g. Catalyst E was obtained.

EXAMPLE 6

For the 5 catalysts A to E, the volumes of chemisorbed CO was determinedusing a dynamic procedure at 20° C. The volumes of chemisorbed CO shownin Table 1 are expressed in cm³/g of Pd.

TABLE 1 Values of chemisorbed CO volumes Catalyst A B C D E Volume of CO70 230 190 199 200 cm³/g Pd

PPTR analysis of catalysts A, B, C and D was carried out using theprotocol described above. FIGS. 1A to 1D show the Programmed TemperatureReduction profiles for catalysts A, B, C and D.

The PTR profiles for catalysts B and C were in accordance with theinvention and exhibited:

a single “low temperature” reduction peak (T<300° C.);

the absence of hydrogen production linked to decomposition of palladiumhydrides.

In contrast, the catalysts with reference numbers A and D exhibited aplurality hydrogen consumption signals at least one of which was at atemperature of over 300° C. The PTR profile of catalyst A also containeda hydrogen production peak at a temperature close to 70° C.

Catalyst E showed a PTR profile analogous to that of catalyst D.

EXAMPLE 7

The characterization by EXAFS of catalysts B and E showed, for catalystE, the presence of oxygen in the near environment of the palladium(first neighbour), whereas, for catalyst B, the palladium is surroundedonly by other palladium atoms. These oxygene atoms, which can only beprovided by the alumina support, indicate that there is a link (hence, arather strong interaction) between palladium present on catalyst E andits support. By contrast, an analogous reasoning shows that there is no(or little) interaction between the palladium present on catalyst B andits support. This distinction could be attributed to the differences inthe preparation techniques used.

EXAMPLE 8

The hydrogenating properties of catalysts A to E were evaluated using aperfectly stirred “Grignard” type batch test. Two grams of palladiumbased catalyst were reduced for 2 hours at 200° C. in a stream ofhydrogen, then transferred to the hydrogenation reactor under an inertgas. The feed to be hydrogenated was a mixture containing 12 g of adiolefin (1,3-butadiene) diluted in 180 cm³ of n-heptane (in thishydrogenation, 1,3-butadiene is converted to 1-butene). The testtemperature was kept at 20° C. and the pressure at 1 MPa. The resultsare shown in Table 2. The hydrogenating activity is expressed in mol.min⁻¹. g Pd.

TABLE 2 Catalytic performances for 1,3-butadiene hydrogenation CatalystA B C D E Activity (mol.min⁻¹ g Pd⁻¹) 4.25 8.75 6.35 1.6E-03 2.0E-01cm³/g Pd Selectivity, % of 1-butene at 59 55 58 60 59 80% of butadieneconversion

Catalyst B was twice as active as reference catalyst A, while a highselectivity to 1-butene is maintained.

For the same support and similar volumes of chimisorbed CO per gram ofpalladium, the activity of catalyst B is markedly higher than that ofcatalyst E (x44) and the activity of catalyst C is considerably higherthan that of catalyst D (x4000).

EXAMPLE 9

The hydrogenating properties of catalysts A, B and E were evaluatedusing a perfectly stirred “Grignard” type batch test. Two grams ofpalladium based catalyst were reduced for 2 hours at 200° C. in a streamof hydrogen, then transferred to the hydrogenation reactor under aninert gas. The feed to be hydrogenated was a mixture containing 13 g ofphenylacetylene diluted in 180 cm³ of n-heptane (in this hydrogenation,phenylacetylene is converted to styrene). The test temperature was keptat 17° C. and the pressure at 1 MPa. The results are shown in Table 3.The hydrogenating activity is expressed in mol. min⁻¹. g Pd⁻¹.

TABLE 3 Catalytic performances for phenylacetylene hydrogenationCatalyst A B E Activity (mol.min⁻¹ g Pd⁻¹) 1.15 1.29 0.3 Selectivity, %of styrene at 97.5 96 95 80% of phenylacetylene conversion

In this case too, the specific activity of catalyst B was higher thanthat of reference catalysts A and E, while a high selectivity to styrenewas maintained.

The above examples can be repeated with analogous results bysubstituting the general or particular reactants and/or conditionsdescribed in the invention for those used in these examples.

The above description will enable the skilled person to readilydetermine the essential characteristics of the invention and, withoutdeparting from the spirit and scope thereof, to make a variety ofchanges or modifications to adapt it to a variety of uses andimplementation conditions.

What is claimed is:
 1. A catalyst comprising a support and an active phase, wherein the support comprises carbon at least one zeolite, or at least one refractory oxide and, wherein the active phase comprises at least one metal from group VIII of the perodic table of the elements, wherein the metal has a dispersion of at least 80%, and wherein said catalyst exhibits a programmed temperature reduction profile comprising a single hydrogen consumption peak at a temperature range of from 50° C. to 300° C.
 2. A catalyst according to claim 1, wherein said support comprises at least one refractory oxide selected from oxides of metals from groups IIA, IIIA, IVB and IVA of the periodic table, used alone or as a mixture, or mixed with oxides of other metals from the periodic table.
 3. A catalyst according to claim 2, wherein the at least one refractory oxide is an oxide of magnesium, aluminum, silicon, titanium, zirconium, or thorium.
 4. A catalyst according to claim 2, wherein the metal from group VIII of the periodic table is iridium, nickel, palladium, platinum, rhodium or ruthenium, in a percentage in the range 0.01% to 10%.
 5. A catalyst according to claim 4, further comprising at least one additional element in the active phase of the catalyst in a percentage in the range 0.01 % to 10%, wherein the additional element is selected from the group consisting of alkali metals, alkaline-earth metals and metalloids.
 6. A catalyst according to claim 1, wherein said support comprises carbon.
 7. A catalyst according to claim 6, wherein the metal from group VIII of the periodic table is iridium, nickel, palladium, platinum, rhodium or ruthenium, in a percentage in the range 0.01% to 10%.
 8. A catalyst according to claim 7, further comprising at least one additional element in the active phase of the catalyst in a percentage in the range 0.01% to 10%, wherein the additional element is selected from the group consisting of alkali metals, alkaline-earth metals and metalloids.
 9. A catalyst according to claim 1, wherein said support comprises at least one molecular sieve selected from the group consisting of X zeolite, Y zeolite, inordenite, faujasite, ZSM-5 zeolite, ZSM-4 zeolite, and ZSM-8 zeolite.
 10. A catalyst according to claim 9, wherein said support further comprises at least one oxide of a metal from groups IIA, IIIA, IVB and IVA of the periodic table.
 11. A catalyst according to claim 9, wherein the metal from group VIII of the periodic table is iridium, nickel, palladium, platinum, rhodium or ruthenium, in a percentage in the range 0.01% to 10%.
 12. A catalyst according to claim 11, further comprising at least one additional element in the active phase of the catalyst in a percentage in the range 0.01% to 10%, wherein the additional element is selected from the group consisting of alkali metals, alkaline-earth metals and metalloids.
 13. A catalyst according to claim 1, wherein the metal from group VIII of the periodic table is iridium, nickel, palladium, platinum, rhodium or ruthenium, in a percentage in the range 0.01 % to 10%.
 14. A catalyst according to claim 13, further comprising at least one additional element in the active phase of the catalyst in a percentage in the range 0.01% to 10%, wherein the additional element is selected from the group consisting of alkali metals, alkaline-earth metals and metalloids.
 15. A catalyst according to claim 1, further comprising at least one additional element in the active phase of the catalyst in a percentage in the range 0.01% to 10%, wherein the additional element is selected from the group consisting of alkali metals, alkaline-earth metals and metalloids.
 16. In a process comprising subjecting an olefinic cut to selective hydrogenation in contact with a catalyst, the improvement wherein the catalyst is in accordance with claim
 1. 17. A process according to claim 16 in which a feed consisting essentially of a hydrocarbon cut from a steam cracker containing 5 to 12 carbon atoms per molecule is treated at an average temperature in the range 25° C. to 200° C., at a pressure in the range 0.1 to 10 MPa and with a molar ratio of hydrogen to hydrocarbons in the range 1 to
 150. 18. A process according to claim 16, in which the catalyst used has an alumina support the specific surface area of which is in the range 5 to 400 m² per gram and which comprises platinum and/or palladium as the group VIII metal.
 19. A catalytic hydrogenolysis process comprising conducting the hydrogenolysis at a temperature in the range 400° C. to 800° C., at a pressure in the range 0.1 to 2 MPa with a molar ratio of hydrogen to hydrocarbons in the range 0 to 20, and in contact with a catalyst according to claim
 1. 20. A process for hydrogenating hydrocarbons containing alkyne, diene or olefin functions, or aromatic functions, comprising conducting the hydrogenation at an average temperature in the range 10° C. to 400° C. and at a pressure in the range 0.1 to 10 MPa, and in contact with a catalyst according to claim
 1. 21. A process for hydrogenating aldehyde, ketone, ester, acid or nitro functions, comprising conducting the hydrogenating at an average temperature in the range 10° C. to 500° C. and at a pressure in the range 0.1 to 10 MPa, and in contact with a catalyst according to claim
 1. 22. A process according to claim 21, in which the catalyst has a silica, carbon or alumina support and comprises rhodium and/or ruthenium as the group VIII metal. 